Injection blow molding machines, such as disclosed in U.S. Pat. No. 4,076,484 having the same assignee as the present invention, are well known in the art for forming hollow articles, particularly containers of various sizes and shapes. Thermoplastic materials such as polypropylene or polyethylene are heated to a molten, semi-fluid state and are injected into the cavity of an injection mold to form a parison over a removable core or parison pin. Before the material has had an opportunity to completely set, the parison thereon is removed from the injection mold and transferred to a blow mold where pressurized gas or air is blown through the pin to the interior of the parison. This gas causes the parison to expand outwardly in the larger cavity of the blow mold. The expanded parison takes the shape of the blow mold cavity corresponding to a desired shape of the article, and is allowed to set sufficiently to retain that shape thereafter.
In containers of the kind envisioned in the present invention, a highly detailed mouth area is injection molded integrally with a parison portion. The parison portion is then blow molded to the dimensions of the body portion of the finished container. In doing so, a transitional surface is formed between the injection molded mouth area and the larger diameter body portion, which appears as an annular groove on the outside surface of the container just below the mouth area. A container of this kind is illustrated in FIG. 1 of my U.S. Pat. No. 3,977,563.
In such containers, there is a requirement for high hoop strength in the mouth area. For this reason, one or more reinforcing ribs have previously been provided as features of the detail of high definition in the injection molded mouth area. The necessity for the provision of such ribs has limited the utility of such containers in that they can only be opened with the aid of a tool. Like the conventional metal containers for paint and the like, a bladed tool such as a conventional screwdriver or putty knife must be used to pry up a lid affixed to the container. Not only is such a requirement often inconvenient for the user, such a metal tool may easily damage the seal area, causing leakage on resealing. This is particularly disadvantageous if the pail is to be used for mixing color tints or the like on a mechanical shaker.
In my copending U.S. patent application Ser. No. 186,675, filed Sept. 12, 1980, I have disclosed a container in which an annular depending skirt has been provided as a feature of the detail of high definition in the injection molded mouth area. This depending skirt provides an outside wall over the transitional surface formed between the injection molded mouth area and the larger diameter blown body portion. This additional feature allows the use of such containers on conventional labeling and bailing machinery interchangeably with conventional containers. In addition, it was recognized that this additional feature increased the wall strength in the region of the transitional surface between the injection molded preform and the blown parison.
It is an object of the present invention to provide a container from which an affixed lid may be removed without the use of a tool.
The objects, features, and advantages of the present invention are pointed out with particularity in the claims annexed to this specification. Further, they will become more apparent in light of the following detailed description of the preferred embodiment thereof and as illustrated in the accompanying drawing.
According to the present invention, there is provided in a container having an injection molded annular mouth portion having detail of high definition, including at least one circumferential reinforcing rib, a generally cylindrical body portion blow molded from a parison portion injection molded integrally with the mouth portion, said body portion having a closed bottom and an inside diameter slightly larger than the inside diameter of the mouth portion, an annular reinforcing region joining the mouth portion to the body portion and forming a transitional surface therebetween, an annular depending skirt provided as a feature of the detail of high definition in the injection molded annular mouth portion, which depending skirt provides an outside wall over said reinforcing region, an improvement comprising at least one gap in the uppermost circumferential reinforcing rib whereby manual removal of an attached lid can be accommodated without the need for a tool.